Distribution of NADPH-d and nNOS-IR in the thoracolumbar and sacrococcygeal spinal cord of the guinea pig

The distribution of NADPH-d staining and neuronal nitric oxide synthase (nN OS)-immunoreactivity in the spinal cord of the guinea pig was studied to ev aluate the potential role of nitric oxide in lumbosacral afferent and spina l autonomic pathways and to compare the distribution of these two markers t o that observed in other species. NADPH-d staining and nNOS-immunoreactivit y were present in neurons and fibers in the superficial dorsal hem, dorsal commissure and in neurons around the central canal in all levels of the spi nal cord examined. Sympathetic preganglionic neurons in the thoracic and ro stral lumbar segments identified by choline acetyl transferase (ChAT) immun oreactivity exhibited prominent NADPH-II staining and nNOS-immunoreactivity ; whereas the ChAT-immunoreactive parasympathetic preganglionic neurons in the sacral segments were not stained. The most prominent NADPH-d staining i n the sacral segments occurred in fibers extending from Lissauer's tract th rough laminae I along the lateral edge of the dorsal horn to the region of the sacral parasympathetic nucleus (lateral collateral pathway of Lissauer) . These fibers were prominent in the S1-S3 segments but not in adjacent (L5 -L7 and Cx1) or thoracolumbar segments. These NADPH-d fibers were, for the most part, not nNOS-immunoreactive, but did overlap with a prominent fiber bundle containing vasoactive intestinal polypeptide immunoreactivity in the sacral spinal cord. These results indicate that nitric oxide may function as a transmitter in thoracolumbar sympathetic preganglionic neurons, but no t in sacral parasympathetic preganglionic neurons. Although the functional significance of the NADPH-d positive, nNOS-negative fiber bundle on the lat eral edge of the sacral dorsal horn remains to be determined, this fiber tr act may represent, in part, visceral afferent projections to the sacral par asympathetic nucleus. (C) 1999 Elsevier Science B.V. All rights reserved.